The present invention relates generally to lost motion devices for internal combustion engine valve controllers and, in particular, to a spool valve lost motion valve deactivation apparatus with an integral accumulator.
Internal combustion engines are well known. Internal combustion engines include a valvetrain having intake and exhaust valves disposed in the cylinder head above each combustion cylinder. The intake and exhaust valves connect intake and exhaust ports with each combustion cylinder. The intake and exhaust valves are generally poppet-type valves having a generally mushroom-shaped head and an elongated cylindrical stem extending from the valve head. A spring biases the valve head in a fully closed position against a valve seat in the cylinder head. Historically, engine valves were actuated from the fully closed position to a fully open position by an underhead camshaft, pushrod, and rocker arm assembly. Hydraulic lifters, which utilize pressurized hydraulic fluid to actuate a piston to reciprocate the valve, were added as a buffer between the motion of the rocker arm and the valve stem and as a means for adjusting valve lash. In later developments, overhead camshafts eliminated the pushrod and, occasionally, the rocker arm for a more direct actuation of the valves.
Devices for deactivating engine valves, known in the art as lost motion devices, are also well known. Lost motion devices are advantageous because they increase the efficiency of the engine by either completely eliminating or reducing the stroke of the valve, thereby allowing no or reduced fuel-air mixture or engine exhaust to enter or exit the cylinder respectively. Many prior art hydraulic lost motion devices are capable of reducing the lift and/or duration of a cam lobe event which is transmitted to the engine valve. These devices are typically controlled by a solenoid valve, and the loss of cam motion is accomplished by the dumping of oil out of a hydraulic link between the cam and the valve in a controlled manner. This has two primary disadvantages which have made these systems unacceptable for volume production. The first disadvantage is energy consumption, since the oil is typically pumped by the cam through a small solenoid valve, with excessive energy losses. This energy is taken out of the crank, and results in a fuel economy loss. The second failing of most lost motion systems is that because the devices use only a portion of the cam lobe, the opening and closing ramps are lost, which results in unacceptably high opening and closing acceleration rates, causing noise, wear, valve bounce, and high frequency stresses. Another concern with prior art lost motion devices is the hydraulic pressures at which they must operate, inevitably making the control solenoid large, causing high power consumption, and rendering the solenoid unable to open against extremes of oil pressure.
In addition, there is an increased interest in the ability of modem microcontrollers to control added engine valve events beyond those of a conventional camshaft, for example, to operate homogeneous charge compression ignition (HCCl) engines, to controlling diesel NOx emissions, and for compression brakes. In the case of NOx control, the strategy is to add an extra intake valve event during the exhaust stroke, or an added exhaust valve event on the intake stroke for the purpose of delivering added residual gas to the next combustion event. In the case of the compression brake, the strategy is to modulate an exhaust valve event at the top of the compression stroke to dump the compression energy to serve as a retarder. In the case of HCCl, one strategy for the control of HCCl ignition is to deliver exhaust to the cylinder in modulated amounts (extra exhaust event on the intake stroke) to control the cylinder temperature and possibly active radical chemistry as an ignition timing control.
It is desirable, therefore, to provide a lost motion apparatus that is adapted to provide a full valve event (the conventional valve event as well as the added event), to provide deactivation of the valve event (as when residual is not required) or to provide accurate modulation between these extremes for controlling the residual rate.